I went back for a short time after my oldest was born and pumped for him. Some things that helped me were:
* remember to drink a lot of water
* eat oatmeal for breakfast (seriously, I noticed getting an extra oz or so if I did this!)
* try pumping 20 minutes instead of just 15, sometimes I would get another letdown which would mean an extra oz or two of milk
* get a picture of the baby and concentrate on that rather than on the pump...really think about the baby's smell, soft fuzzy hair, how sweet he/she is, etc., and how even though I could not be with him at the time, I could do this for him
* do breast compressions while pumping...sometimes that would help
* to get extra sessions in, try pumping one side and nursing on the other when at home
And remember, ANY breastmilk the baby gets is awesome! Pumping is hard work, and I commend all of you for even trying it!